Murine respiratory mycoplasmosis (MRM) is but one of many intercurrent diseases in laboratory rats and mice; however, it is unrivaled as THE major disease problem encountered in chronic rodent studies. The losses incurred due to wasted man hours and unusable research data are staggering when one considers the continued high incidence of the disease in animal research facilities and the fact that rats and mice account for approximately five-sixths of all laboratory animals used annually in the U.S. These facts become even more impressive in view of our recentfinding that Mycoplasma pulmonis, the etiological agent of MRM, also causes a chronic genital infection which can lead to a 50-100% reduction in birth rate. Thus, there is a critical need for practical methods to control this infection in order to eliminate its detrimental effects on the research process. Recent developments in our laboratory now permit a direct attack on this problem. All lesions of natural MRM and genital mycoplasmosis have been reproduced by inoculation of pure cultures of M. pulmonis into animals reared and maintained so as to exclude all other pathogens. An enzyme-linked immunosorbent assay (ELISA), which offers promise as a simple, rapid diagnostic procedure, has been developed for detection of M. pulmonis antibodies. Also, both rats and mice have been shown to be effectively protected from MRM by vaccination with live or formalin-killed organisms. The goals of the present research program are: 1) to evaluate the ELISA for large-scale screening purposes; 2) to further define the epidemiology of murine respiratory and genital mycoplasmoses in order to facilitate detection and elimination of infected animals; and 3) to fully evaluate the efficacy of formalin-killed organisms as a means of controlling disease in certain specified animal populations. These studies are expected to result in control measures of immediate practical value to producers and users of laboratory rats and mice.